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Java 8 : Date and Time - Part I


Wikipedia defines Time as:

"Time is a measure in which events can be ordered from the past through the present into the future, and also the measure of durations of events and the intervals between them.Time is often referred to as the fourth dimension, along with the three spatial dimensions."

Since Time is a natural concept, in an ideal world, dealing with it should be simple, but unfortunately it is not the case and we humans made it more complex by introducing different time zones and day light saving.

As a programmer, we want that programming languages immune us from these complexity and being a Java programmer, we have similar expectations from Java. Java tried to overcome these complexities in its first two editions of Date and Time API, but failed measurably. A simple google will give you numerous posts criticizing Java for this. Few years back, I was introduced to Joda-Time library that provide APIs that help you to work with Time with ease.

In its latest edi…
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Exploring Java 7 : Try-with-resources

Try-with-Resource is new featured added in Java 7. Personally, I like this feature very much, as it helps to reduce a lot of boiler plate code.

Consider a scenario, where we have to release a system resource, like JDBC Connection or File Stream. Prior to Java 7, it meant that developer has to write a lot of boiler plate code to release that resource. In order to ensure releasing of resource in all the situations, one has to use finally block as well for exception cases. Consider following example, written with Java 6:

String readFirstLine(String path) throws IOException { BufferedReader br = new BufferedReader(new FileReader(path)); try { return br.readLine(); } finally { if (br != null) br.close(); } } Clearly, one has to write almost 4-5 lines for closing each resource. Now, what Java 7 did is that it made the process of closing resource automatic.

In Java 7, a resource is defined as "An object of type java.lang.AutoCloseable.". This AutoCloseable interfa…

Interface or Abstract Class

What is the difference between an Abstract Class and an Interface?
Well, isn't it an interesting question or for few, a foolish question?

For a number of Java newbies, the only difference between two is, "You can't have method body in Interface.". Well, I would say that it is technically (Implementation vise) correct, but doesn't reflect the concept.

Abstract Class
An abstract class, is the most generalized form of an Entity hierarchy (In Java, a Class is an entity), such that it doesn't represent a real entity on its own, but provides a basis on which real entities can be build within that hierarchy. An abstract class provides a default behavior and also provide abstract behavior (Operations that must be override by the real classes).

An interface, on the other hand is a contract that states that you have to agree to provide following operations if you agree to abide by me, i.e. an entity that agrees to abide by the contract of interface, will have t…

Singleton Pattern: Am I implementing it Correctly? - Part II

In my last post, I discussed implementation of Singleton Pattern in a Single Threaded Environment. There was a very good discussion on whether about very existence of this pattern as well. Actually it is an ever going debate, few people think that it is an anti pattern and few think it is a simple solution of a common problem.

My intent of this post (and previous also) is to discuss on how to implement it, rather than whether to use it!!! So, let's start discussing Singleton Pattern in a Multi-threaded environment.

Singleton Pattern in Multi-Thread environment:

We have seen using static factory to implement Singleton Pattern in a single thread environment and also discussed problems associated with it. When in Multi-threaded environment, there are other problems as well.

What will happen if two threads simultaneously try to access static factory method (getInstance() method)? It will result in two instance of class, though we required only one instance. Clearly, singleton pattern …

Singleton Pattern: Am I implementing it Correctly? - Part I

Novice way to implement a Singleton:
I believe everyone starts (and even continues to do so) implementing Singleton pattern in following fashion:
package com.singleton; public class SimpleSingleton { private static SimpleSingleton simpleSingleton; private SimpleSingleton() { }; public static SimpleSingleton getInstance() { if (simpleSingleton == null) simpleSingleton = new SimpleSingleton(); return simpleSingleton; } }
Do you find any problem in it?
Well, I have!!! The contract of Singleton class can be broken. 
Let's discuss Singleton pattern in Simple Threaded environment and then in next post I will discuss this pattern in Multithreaded environment.

In a Single Threaded Environment:
Do you remember the double edge sword in Java, "REFLECTION"?
With the help of reflection, one can very easily breach the singleton contract for above class and create as many instance as he wants. Let's consider following three statements:
//Get Private Constructor Constructo…


Every Java Program can attach a shutdown hook to JVM, i.e. piece of instructions that JVM should execute before going down.

A program may require to execute some pieces of instructions when application goes down. An application may go down because of several reasons:
Because all of its threads have completed executionBecause of call to System.exit()Because user hit CNTRL-CSystem level shutdown or User Log-OffFew scenarios where this requirement fits are:
Saving application state, e.g. when you exits from most of the IDEs, they remember the last viewClosing some database connectionsSend a message to System Administrator that application is shutting down.Solution:
Shutdown Hook comes to rescue in all such scenarios. Application attach a shutdown hook to thereself, that JVM runs when application goes down.

Concept at Abstract level:
Write all the instructions(java code) in a thread's run method and call java.lang.Runtime.addShutdownHook(Thread t). This method will then …

Remote debugging in Java

Buzz Word: Remote Debugging
Consider a scenario where you can't run the application in your development environment, e.g. say your application can run only on a server machine (because it is dependent on some third party interface that are not accessible in your development machine) and you have to resolve a problem (bug). What you can do?

The solution is Remote debugging. Remote debugging is debugging an application by connecting the remotely running application with your development environment ( i.e. you can say to connect with code in your IDE).

How it works : Basic concept
Remote debugging feature is provided by Java specification itself. Java provides this feature using listener binding mechanism. Basic concept is pretty simple and straightforward:
Application to be debugged would attach a socket to itself and then would listen debug instructions on that socket.Debugger would bind itself to that socket and then send instructions on that socket.Running an application in debug mo…